Conventionally, conductive porous materials processed by expanding, etching, or punching are used as an electrode and electrode base material which are used for an electrolytic cell, a cell, etc.
For example, as the base material of an anode of an electrochemical cell used to produce sodium hydroxide, a catalyst-coated titanium mesh in which a titanium plate of a mesh structure is coated with a catalyst, is used.
The titanium plate of mesh structure functions not only as a carrier of a catalyst, but also a diffusion path for a material to be reacted, such as a gas, and a feeding member.
The reaction formulas involved in the production of sodium hydroxide manufacture are as follows.
Reaction at cathode 2H2O+2e−→H2+2OH
Reaction at anode 2Cl−→Cl2+2e−
Overall reaction 2H2O+2NaCl→2NaOH+Cl2+H2 
The reason for using titanium as a base material of the anode in the production of sodium hydroxide manufacture is because the anode potential becomes very high. When stainless steel, copper, nickel or the like is used as the base material of the anode and the anode potential becomes high, an elution may occur.
When selecting a base material in terms of properties, it is desirable to select one which does not elute easily if the electrode is exposed to an electrical potential involved in a desired reaction. For example, usable examples of the base material for the cathode, which can produce hydrogen in the above-provided reaction formula are stainless steel, copper and carbon in addition to titanium.
In the above-listed examples, porous materials are indicated as base materials, but it is also possible to use a material which has a catalytic effect by itself, such as Pt, Ni or Pd, as a porous material by processing the material into a porous structure, as a porous electrode.
Here note that in the case where a great number of pores are to be opened in a base material of a conductive plate having a certain thickness by a method applicable to mass-production, such expanding, etching or punching, as the thickness of the base material is less, it becomes possible to process the material to have smaller pores in diameter by the method. Generally, it is more difficult to shorten the distance between openings than to make the base material thin due to the processability (workability). Therefore, in the case where pores should be opened as many as possible per unit area (the concentration of pores should be increased), the thinner the base material, the more advantageous because the distance between openings is smaller in thinner base materials.
Electrodes which employ a base material of such a porous structure are used for, for example, electrodes of zero-gap electrochemical cells. In a zero-gap electrochemical cell, an electrode is disposed to tightly attach to the solid electrolytic membrane without any gap.
The electrochemical reaction in the electrochemical cell occurs in the interface between the electrolytic membrane through which ions can move and the catalyst.
As to the movement of materials subjected to reaction and products thereof, the shorter the distance between openings, the shorter the distance in which they move a narrow path made by the electrolytic membrane and the electrode tightly attached to each other. Here, since the diffusion resistance is suppressed more as the diffusion distance is shorter, the voltage applied to the electrochemical cell is decreased.
Moreover, the reaction area can be listed as another important factor for progress of a reaction in an electrochemical cell. A reaction area becomes larger, as the porosity of the electrode employing the base material of a porous structure is less. For this reason, it is more advantageous when the base material of the electrode is thinner because for the same porosity, the higher the concentration of pores, the higher the rate of reaction realizable.
It should be noted that, when the base material of an electrode is thin, the conduction path of the base material itself becomes narrow, and it is expected that the collector resistance increases. To avoid this, there has been such an attempt to join a collector plate and a feed plate to the electrode base material having a mesh structure, so as to lower the collector resistance.
However, if this structure allows electrolytic ions to enter the collector plate and feed plate, it is necessary to select, for the collector plate and feed plate, materials which do not elute with an electrical potential by which the reaction is occurring (to be called a reaction potential hereinafter) as in the case of the base material for the electrode.
Further, even the materials which do not elute at the reaction potential may increase the contact resistance with respect to the electrode, if the collector plate and feed plate are formed of a material with which an oxide layer is formed on its surface, such as titanium or aluminum. To avoid this, it is necessary to coat the surface of the material which forms the collector plate and feed plate with a corrosion resistance substance so that the material for the collector plate and feed plate is not oxidized as brought into direct contact with the electrode.
For example, the anode of an electrolytic cell configured to electrolyze water is exposed to a potential higher than 1.23VvsRHE. For this reason, it is required to use such an anode that the surface of titanium, which gives rise to a conductive plate or feed plate, with platinum (Pt), which does not easily elute at such an electrical potential, by sputtering or plating.
An object of the embodiments is to provide an electrochemical cell which can improve both the rate of reaction at an interface with an electrolytic membrane and the feeding performance, and does not easily corrode by the reaction potential by a simple structure, an oxygen reduction device using the cell, and a refrigerator using the oxygen reduction device.